Volume 16 (1997)
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Item Network Services(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item EG Eurographics ' 97: Annual Conference of the European Association for Computer Graphics(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item A Flexible Architecture for Virtual Humans in Networked Collaborative Virtual Environments(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sunday Pandzic, Igor; Lee, Elwin; Magnenat Thalmann, Nadia; Capin, Tolga K.; Thalmann, DanielComplex virtual human representation provides more natural interaction and communication among participants in networked virtual environments, hence it is expected to increase the sense of being together within the same virtual world. We present a flexible framework for the integration of virtual humans in networked collaborative virtual environments. A modular architecture allows flexible representation and control of the virtual humans, whether they are controlled by a physical user using all sorts of tracking and other devices, or by an intelligent control program turning them into autonomous actors. The modularity of the system allows for fairly easy extensions and integration with new techniques making it interesting also as a testbed for various domains from "classic" VR to psychological experiments. We present results in terms of functionalities, example applications and measurements of performance and network traffic with an increasing number of participants in the simulation.Item A Million Polygons, a Million Pixels: Which is Heavier?(Blackwell Publishers Ltd and the Eurographics Association, 1997) Sillion, Francois X.The impressive progress of rendering software and hardware over the last two decades often leads to the - too rapid - conclusion that high-quality 3D imagery can now be incorporated in all sorts of applications. Interestingly, these advances allow more and more complex applications to be envisioned: however, an increase in processing power is not necessarily used to treat the same problem faster, but also creates a desire to attack larger problems. In many ways the models for visual simulation or engineering applications grow faster than the graphics systems! recent work on image-based rendering and modeling shows a growing awareness that traditional 3D methods may not scale well for the current and coming complexity levels.This talk will examine some of the challenges lying ahead for the development of future graphics applications. Specifically, when is it better to use pixels than polygons? when is a 3D model required? how can we mix and match competing approaches? can image-based approaches help for different applications such as lighting simulations? some issues related to network applications will also be discussed.Item Tunnel-Free Supercover 3D Polygons and Polyhedra(Blackwell Publishers Ltd and the Eurographics Association, 1997) Andres, Eric; Nehlig, Philippe; Francon, JeanA new discrete 3D line and 3D polygon, called Supercover 3D line and Supercover 3D polygon, are introduced. Analytical definitions are provided. The Supercover 3D polygon is a tunnel free plane segment defined by vertices and edges. An edge is a Supercover 3D line segment. Two different polygons can share a common edge and if they do, the union of both polygons is tunnel free. This definition of discrete polygons has the "most" properties in common with the continuous polygons. It is particularly interesting for modeling of discrete scenes, especially using tunnel-free discrete polyhedra. Algorithms for computing Supercover 3D Lines and Polygons are given and illustrated.Item Synthesizing Novel Views from Unregistered 2-D Images(Blackwell Publishers Ltd and the Eurographics Association, 1997) Havaldar, Parag; Lee, Mi-Suen; Medioni, GerardSynthesizing the image of a 3-D scene as it would be captured by a camera from an arbitrary viewpoint is a central problem in Computer Graphics. Given a complete 3-D model, it is possible to render the scene from any viewpoint. The construction of models is a tedious task. Here, we propose to bypass the model construction phase altogether, and to generate images of a 3-D scene from any novel viewpoint from prestored images. Unlike methods presented so far, we propose to completely avoid inferring and reasoning in 3-D by using projective invariants. These invariants are derived from corresponding points in the prestored images. The correspondences between features are established off-line in a semi-automated way. It is then possible to generate wireframe animation in real time on a standard computing platform. Well understood texture mapping methods can be applied to the wireframes to realistically render new images from the prestored ones. The method proposed here should allow the integration of computer generated and real imagery for applications such as walkthroughs in realistic virtual environments. We illustrate our approach on synthetic and real indoor and outdoor images.Item A Multiscale Approach to Integrated Volume Segmentation and Rendering(Blackwell Publishers Ltd and the Eurographics Association, 1997) Westermann, Rudiger; Ertl, ThomasA number of techniques have been proposed for rendering volumetric scalar data sets. Techniques have also been proposed for analyzing the three dimensional information contents of the underlying domain, but traditionally the data analysis part is left as a post-processing step which only involves the rendered two dimensional images. In this paper, we describe a visualization method for scalar volume data which integrates explicit knowledge of the underlying domain into the rendering process. The key of this approach lies in a hierarchical description of the discrete signal, which is decomposed into a sequence of multiscale representations. We describe a technique for the analysis of structures within the data. This allows for the segmentation and classification of the relevant features and can be used to improve their visual sensation. We also address the problem of accelerating the final rendering pass by integrating the extracted object space information into the ray traversal process.Item An Algorithmic Reflectance and Transmittance Model for Plant Tissue(Blackwell Publishers Ltd and the Eurographics Association, 1997) Baranoski, Gladimir V.G.; Rokne, Jon G.Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.Item Calender of Events(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Orthogonal Decomposition of Non-Uniform Bspline Spaces using Wavelets(Blackwell Publishers Ltd and the Eurographics Association, 1997) Kazinnik, Roman; Elber, GershonWe take advantage of ideas of an orthogonal wavelet complement to produce multiresolution orthogonal decomposition of nonuniform Bspline (NUB) spaces. The editing of NUB curves and surfaces can be handled at different levels of resolutions.Applying Multiresolution decomposition to possibly C1 discontinuous surfaces, one can preserve the general shape on one hand and local features on the other of the free-form models, including geometric discontinuities. The Multiresolution decomposition of the NUB tensor product surface is computed via the symbolic computation of inner products of Bspline basis functions. To find a closed form representation for the inner product of the Bspline basis functions, an equivalent interpolation problem is solved.As an example for the strength of the Multiresolution decomposition, a tool demonstrating the Multiresolution editing capabilities of NUB surfaces was developed and is presented as part of this work, allowing interactive 3D editing of NUB free-form surfaces.Item An Analysis of Quasi-Monte Carlo Integration Applied to the Transillumination Radiosity Method(Blackwell Publishers Ltd and the Eurographics Association, 1997) Szirmay-Kalos, Laszlo; Foris, Tibor; Neumann, Laszlo; Csebfalvi, BalazsThis paper presents an enhanced transillumination radiosity method that can provide accurate solutions at relatively low computational cost. The proposed algorithm breaks down the double integral of the gathered power to an area integral that is computed analytically and to a directional integral that is evaluated by quasi-Monte Carlo techniques. Since the analytical integration results in a continuous function of finite variation, the quasi-Monte Carlo integration that follows the analytical integration will be efficient and its error can be bounded by the Koksma-Hlawka inequality. The paper also analyses the requirements of the convergence, presents theoretical error bounds and proposes error reduction techniques. The theoretical bounds are compared with simulation results.Item Book Reviews(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Implicit Representations of Rough Surfaces(Blackwell Publishers Ltd and the Eurographics Association, 1997) Hart, John C.Implicit surface techniques provide useful tools for modeling and rendering smooth surfaces. Deriving implicit formulations for fractal representations extends the scope of implicit surface techniques to rough surfaces. Linear fractals modeled by recurrent iterated function systems may be defined implicitly using either geometric distance or escape time. Random fractals modeled using Perlinâ s noise function are already defined implicitly when described as "hypertexture."Deriving new implicit formulae is only the first step. Unlike their smooth counterparts, rough implicit surfaces require special rendering techniques that do not rely on continuous differentiation of the defining function. Preliminary experiments applying blending operations to rough surfaces have succeeded in an initial attempt to overcome current challenges in natural modeling. The grafting of a stem onto the base of a linear fractal leaf continuously blends smooth detail into rough detail. The blend of two textured cylinders interpolates geometric bark across branching points in a tree.Item Selective Pixel Transmission for Navigating in Remote Virtual Environments(Blackwell Publishers Ltd and the Eurographics Association, 1997) Mann, Yair; Cohen-Or, DanielThis paper presents a technique to improve the performance of a walkthrough in remote virtual environments, where a scene is rendered jointly by the server and the client, in order to reduce the network requirements as much as possible. The client generates novel views by extrapolating a reference view based on the locally available geometric model, while the server transmits data necessary to prevent an accumulation of errors. Within this concept, we show that by transmitting only a selected subset of pixels, the quality of the extrapolated views can be improved while requiring less bandwidth. We focus on the selection process in which the visibility gaps between the reference view and novel view are detected, packed and transmitted compressed to the client.Item Modeling and Rendering of the Atmosphere Using Mie-Scattering(Blackwell Publishers Ltd and the Eurographics Association, 1997) Jackel, D.; Walter, B.This paper presents a method for rendering of the atmosphere by means of Mie-scattering. The method is based on a concentric atmospheric model, which is divided into four submodels: for clear air, aerosol, ozone, and rain. In order to simulate and visualize the various atmospheric effects, each of these submodels can be parameterized by the user as desired. The process of rendering an outdoor scene requires an enormous amount of computing power. In order to make this method suitable for efficient implementation, some simplifications and approximations are discussed. In addition, a selection of the rendering results are presented, and our further activities in the field of atmospheric rendering are discussed.Item Prize Competition: 1998 Cover Photograph(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Preface and Table of Contents (EG 1997, CGF 16-3)(Blackwell Publishers Ltd and the Eurographics Association, 1997) Fellner, Dieter W.; Szirmay-Kalos, László-Item Parallel Progressive Ray-tracing(Blackwell Publishers Ltd and the Eurographics Association, 1997) Notkin, Irena; Gotsman, CraigA dynamic task allocation algorithm for ray-tracing by progressive refinement on a distributed-memory parallel computer is described. Parallelization of progressive ray-tracing is difficult because of the inherent sequential nature of the sample location generation process, which is optimized (and different) for any given image. We report on experimental results obtained from our implementation of this algorithm on a Meiko parallel computer. The three performance measures of the algorithm, namely, load-balance, speedup, and image quality, are shown to be good.Item Eurographics UK Chapter 16th Annual General Meeting: University of East Anglia, Norwich, March 25, 1997(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Eurographics '97: Budapest, Hungary, September 4-8, 1997(Blackwell Publishers Ltd and the Eurographics Association, 1997)